POINT: Global distribution amounts of used and unused mineral extraction generated by iron, copper, and nickel mining were estimated, and linkages between national economies and global impacts were demonstrated.

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In today's global economy, each country has indirect material flows supporting its economic activities in addition to direct ones, and international trade chains cause environmental burdens far removed from the places of consumption. Under these conditions, it is important to examine positive and negative impacts of economic activities as a systemic global phenomenon to manage the burdens far removed from the place of consumption, rather than viewing production and producers in isolation. We examined global distribution amounts of used and unused mineral extraction generated by iron, copper, and nickel mining, and demonstrated linkages between national economies and global impacts based on a global link input-output (GLIO) model which is a hybrid multiregional model. The estimated global amount of used and unused mineral extraction generated by iron, copper, and nickel mining more than doubled from 1990 to 2013. For 2011, we also estimated the amount of total used and unused extraction generated by iron, copper and nickel mining induced by Japan's final demand. Whereas the world total extraction generated by iron, copper, and nickel mining rapidly increased from 2005 to 2011, the extraction amount induced by Japan's final demand for the same period either stayed about the same (iron) or decreased slightly (copper and nickel).

Our analyses on the cumulative amounts of used and unused extraction caused by iron, copper, and nickel mining around the world from 1990 to 2013 suggest that the human activities and processes associating with the mining activities have also occurred during the period. The mining activities and the deposition of mine wastes may cause serious damage on natural capital such as destruction of native vegetation. They may also cause disasters such as tailing dam disasters. Our research findings provide a basis for planning actions to mitigate these issues and to ensure sustainable patterns of resource consumption and production.

POINT: A panel data analysis demonstrated that an increase of base and scarce metal consumption has been associated with deterioration of some indicators measuring a progress of SDGs including social, economic and environmental targets.

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We studied nexus between economy-wide metal inputs and the deterioration of SDGs using panel data at a national scale covering over a ten-year period (2004-2013). The panel data analysis demonstrated the impact of changes in the material flows of 11 metals on 96 SDG indicators corresponding to the 17 SDGs defined by the United Nations. This fact indicates a strong need to decouple metal input from achieving SDGs in countries where metal mining is expanding. In particular, scarce metals are key inputs to new energy technologies such as fuel cells and electric vehicles. Therefore, if the mining of scarce metals continues to expand as part of the global effort for their transition to a low-carbon society, international community should ensure that countries mining scarce metals are able to achieve SDGs in their own right. When metal-mining countries are unable to resolve social problems such as poverty, hunger, and other issues related to health or education on their own, the metal-using countries should ensure that the entire international supply chain supports sustainability of the mining countries by providing technological and monetary assistance to them, and adopting regulations regarding metal procurement responsibilities to navigate us toward the sustainable patterns of resource production and consumption.

POINT: The first systematic review was conducted on long-term dynamics of critical metals for 48 elements, and a comprehensive picture was obtained on the research progress in this field.

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In today's global economy, each country has indirect material flows supporting its economic activities in addition to direct ones, and international trade chains cause environmental burdens far removed from the places of consumption. Under these conditions, it is important to examine positive and negative impacts of economic activities as a systemic global phenomenon to manage the burdens far removed from the place of consumption, rather than viewing production and producers in isolation. We examined global distribution amounts of used and unused mineral extraction generated by iron, copper, and nickel mining, and demonstrated linkages between national economies and global impacts based on a global link input-output (GLIO) model which is a hybrid multiregional model. The estimated global amount of used and unused mineral extraction generated by iron, copper, and nickel mining more than doubled from 1990 to 2013. For 2011, we also estimated the amount of total used and unused extraction generated by iron, copper and nickel mining induced by Japan's final demand. Whereas the world total extraction generated by iron, copper, and nickel mining rapidly increased from 2005 to 2011, the extraction amount induced by Japan's final demand for the same period either stayed about the same (iron) or decreased slightly (copper and nickel).

Our analyses on the cumulative amounts of used and unused extraction caused by iron, copper, and nickel mining around the world from 1990 to 2013 suggest that the human activities and processes associating with the mining activities have also occurred during the period. The mining activities and the deposition of mine wastes may cause serious damage on natural capital such as destruction of native vegetation. They may also cause disasters such as tailing dam disasters. Our research findings provide a basis for planning actions to mitigate these issues and to ensure sustainable patterns of resource consumption and production.

POINT: A total of 70 studies examining long-term outlooks for six major metals were reviewed, and a comprehensive picture was obtained on the research progress in this field.

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Sustainable metal supply requires well-coordinated strategy and policy packages based on a sound scientific understanding of anticipated long-term demand, supply, and associated environmental implications. Such information, however, is highly fragmented among various case studies. Accordingly, this extensive review explores the projected long-term status of six major metals-iron, aluminum, copper, zinc, lead, and nickel-with around 200 data points for global demand through 2030, 2050 and 2100. Our findings show that global demand for these major metals is likely to increase continuously over the 21st century, approximately 2 to 6 fold depending on the metal. Although the extraction and processing required to meet this increase in demand must be environmentally sustainable, the existing extraction and processing scenarios have few explicit linkages to the Earth's carrying capacity. We further found that strategy choices are heavily biased toward end-of-life phase analyses, specifically that of end-of-life recycling. Consequently, a full range of opportunities across entire life cycles are being overlooked, including advances in product design, manufacturing and in-use phases. Importantly, despite the emergence of numerous scenarios, few provide science-based targets for major metal flows, stock, circularity, and efficiency. These knowledge gaps need to be addressed urgently in order to ensure that future research directly supports science-based decision and policy making.

POINT: Global targets for metal flows, stocks, and use intensity in the global economy to 2100 were developed. These targets are consistent with greenhouse gas emission pathways to achieve the 2℃ climate goal and cover six major metals (iron, aluminum, copper, zinc, lead, and nickel).

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Metals underpin essential functions in modern society, yet their production currently intensifies climate change. Global targets for metal flows, stocks, and use intensity in the global economy to 2100 were developed. These targets are consistent with emissions pathways to achieve the 2℃ climate goal and cover six major metals (iron, aluminum, copper, zinc, lead, and nickel). Results indicate that despite advances in low-carbon metal production, a transformative system change to meet the society's needs with less metal is required to remain within the 2℃ pathway. Globally, demand for goods and services over the 21st century needs to be met with approximately 7 t/capita of metal stock, roughly half the current level in high-income countries. This systemic change will require a peak in global metal production by 2030 and deep decoupling of economic growth from both metal flows and stocks. Importantly, the identified science-based targets are theoretically achievable through such measures as efficient design, more intensive use, and longer product lifetime. However, immediate action is crucial before middle- and low-income countries complete full-scale urbanization.

In the figure above, the ranges in the 2℃ scenario are due to differences in assumptions regarding the end-of-life recycling rate and product lifetime. The upper limit of the range (CE scenario) assumes that the end-of-life recycling rate and product lifetime increase to the theoretical maximum by 2100 according to the saturation curve. The lower limit of the range (BAU scenario) represents the assumption that all model parameters are constant throughout the scenario period.

POINT: This research sets out to quantify the mortality and economic loss in individual Asian countries caused by the PM_2.5 emissions induced by the consumption of the world's five highest-consuming countries (US, China, Japan, Germany, UK).

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In 2010 alone, the economic impact of these five countries' consumption caused a loss of almost 45 billion US dollars due to the premature deaths of more than 1 million people in Asia, including 15 thousand children younger than 5 years old. The percentage ratio of economic loss to value-added driven by consumers via trade differed greatly among the impacted countries. For the US, the highest percentage loss was 4.1% in Laos, followed by 2.0% in Bangladesh, both markedly higher than the figures for the more developed countries, such as 0.21% for Japan and 0.18% for Korea. This reflects the inequitable value chain existing between consumer countries and impacted countries, and implies that developing countries are obtaining value-added in exchange for unintentionally increased health risks, delaying their development and potentially creating a vicious circle that hinders much-needed improvements in areas like poverty reduction and public health. This inequitable situation needs to be redressed through introduction of clean energy and other types of technological assistance to help achieve SDGs 7, 10 and 13. Such as move is essential if premature infant deaths are to be curtailed.

In the figure above, color of points denotes percentage ratio of economic loss to value-added in Asian countries induced by consumer countries. Countries in which only premature deaths could be calculated are listed below each chart with their number. Countries with no induced premature deaths are not shown. PPP: purchasing power parity. Country codes are as follows: Afghanistan (AFG), Bangladesh (BGD), Brunei Darussalam (BRN), Bhutan (BTN), China (CHN), Guam (GUM), Hong Kong (HKG), Indonesia (IDN), India (IND), Japan (JPN), Kyrgyz Republic (KGZ), Cambodia (KHM), Korea (KOR), Lao PDR (LAO), Sri Lanka (LKA), Macao (MAC), Maldives (MDV), Myanmar (MMR), Mongolia (MNG), Northern Mariana Islands (MNP), Malaysia (MYS), Nepal (NPL), Pakistan (PAK), Philippines (PHL), Palau (PLW), North Korea (PRK), Singapore (SGP), Thailand (THA), Tajikistan (TJK), Turkmenistan (TKM), Timor-Leste (TLS), Taiwan (TWN), Uzbekistan (UZB) and Vietnam (VNM).

POINT: A model for estimating future WEEE generation was proposed based on the population balance model (PBM), and case studies were conducted to estimate future WEEE generation in Asian countries based on future scenarios of socio-economic indicators and product lifespan.

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We proposed a model for estimating the future WEEE generation based on the PBM. We also developed regression models for estimating the future stock amount of products, which is needed as input data for the proposed model, for air conditioners, refrigerators, washing machines, and mobile phones by using the data for 62 countries including 25 non-OECD countries. Using these models, we conducted case studies of estimating future WEEE generation in Asian countries based on future scenarios of socio-economic indicators and product lifespan. We also conducted another case study on converting the estimated WEEE generation into the amount of contained hazardous substances by using fluorocarbons as an example.¹

Results of our estimation of the amount of fluorocarbons contained in end-of-life (EoL) room air conditioners up to 2030 in Asia are as follows. We found that China had dominant contribution in any items and its estimation would be several times or over ten times those of Japan (e.g., 9.2 times in the case of air conditioners in 2030). We surveyed the transition of refrigerant fluorocarbon types in each of the seven selected Asian countries and calculated the amount of each type of fluorocarbons and their Global Warming Potential (GWP) from EoL air conditioners. Then China again had dominant contribution (approximately 90%) among the seven Asian countries reviewed whose total GWP estimation since 2015 accounted for about 100 to 140 million t-CO₂ equivalent. This suggested the importance of collecting fluorocarbons from EoL air conditioners.

In general, developing countries in Asia do not have a recycling scheme for fluorocarbons that covers their collection and decomposition. Therefore, we estimated the amount of waste refrigerant from EoL air conditioners in order to compare and examine the following two aspects: (i) proper treatment within each country, and (ii) proper treatment with transboundary movement. Then we prepared Decomposition with Transboundary Movement scenario (maximum recovery and decomposition treatment is performed in each country, and if there are not enough existing treatment facilities in the country concerned, cylinders filled with waste refrigerant are transported by ship to Japan for decomposition treatment). The results showed that the capacity of the destruction processing equipment is insufficient in the country concerned when the maximum amount of waste refrigerant is recovered, and in that case, it is more cost-effective to ship the cylinders to Japan and destroy them than to construct a new destruction processing facility. Figure 2 shows the case of China. The costs of mitigating fluorocarbons are estimated around 300-800 JPY/t-CO₂ equivalent (3-8 US$/t-CO₂ equivalent) in 2030 in developing countries. Compared to the costs of achieving the 2℃ target, the costs of recovery and decomposition are more competitive.

POINT: Chemical substances having higher priority in risk management of informal WEEE-dismantling and recycling were identified through their exposure and health risk assessment in Vietnam to mitigate negative environmental impact and improve safety of dismantling workers.

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Our previous studies suggest that hazardous substances, such as polybrominated diphenyl ethers (PBDEs), heavy metals and dioxin-like compounds contained in WEEE, are released to the environment with possible environmental and health risks when their manual dismantling, open storage, and open burning are conducted inadequately.

In this study, in order to identify the chemicals having higher priority in risk management in the WEEE-dismantling areas, we estimated the daily chemical intakes of workers engaged in WEEE dismantling, and assessed their health risks from chemical exposure via indoor dust ingestion or inhalation and intake of free-range chicken eggs. The indoor dust was collected from three dismantling facilities in northern Vietnam in October 2015, and the free-range chicken eggs were obtained from the dismantling workers in November 2017. For all samples, contents of chemicals related with WEEE, namely brominated flame retardants (BFRs) such as PBDEs and tetrabromobisphenol A (TBBPA), phosphorus-containing flame retardants (PFRs) such as tris(2-chloroisopropyl) phosphate (TCIPP) and tris(2-chloroethyl) phosphate (TCEP), heavy metals such as copper, lead and zinc, and dioxin-like compounds, were investigated.

Bioaccessible concentrations of copper, lead, and zinc in the gastric phase and TBBPA, TCEP and TCIPP in the intestinal phases tended to be higher than those of PBDEs and dioxin-like compounds in the intestinal phase. Similar results were obtained in the lung phase with copper, lead, zinc, TBBPA, TCEP and TCIPP showing higher bioaccessibility than PBDEs and dioxin-like compounds. These results suggest that exposure amount of chemicals having relatively high polarity via indoor dust is large if their content is high in dust samples. As for the free-range chicken eggs, high concentrations of PBDEs (mainly decabromo diphenyl ether [decaBDE]) and dioxin-like compounds that persist in the environment were detected in them while concentrations of non-persistent organic chemicals, such as TBBPA, TCEP and TCIPP, and heavy metals were extremely low or not detected. Exposure was estimated from bioaccessible chemical concentrations for dust ingestion and inhalation, chemical concentrations for egg intake, and suitable exposure rates. Indoor dust ingestion² was suggested to be the main contributor to daily intake of lead and copper. Dust inhalation³ was calculated and proved to contribute to daily intake of TBBPA, TCIPP, TCEP, and zinc. Egg intake was anticipated to be a significant contributor to daily intake of decaBDE and dioxin-like compounds.

As shown in Fig. 3, the median-based hazard quotients-namely, the exposures as ratios to tolerable weekly intake, provisional tolerable weekly intake, or reference doses-clearly indicated that large amounts of exposure would increase the potential non-cancer health risks posed by lead and dioxin-like compounds to the WEEE-dismantling workers.

Our findings suggest that the dust emitted to surrounding environment should be controlled, and that measures against the indoor dust exposure should be implemented to reduce adverse health effects of lead and dioxin-like compounds in the WEEE-dismantling areas.

POINT: Flows of plastics originated from WEEE in their recycling process in Japan and the contained brominated flame retardants (BFR) were estimated for the fiscal year (FY) 2017. Although the mixed plastics export from Japan is considered to have decreased after China's waste plastic import ban, recycled pellets from WEEE plastics are still exported to China and other Asian countries. Nevertheless, a large proportion of BFRs were eliminated from the recycled plastics during the sorting processes.

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Recycling of plastics from WEEE has been promoted both in Japan and Europe, but Japan requires much wider adoption of advanced approaches such as their recycling to new electric and electronic equipment (EEE). However, recycling of plastics containing some BFRs at and above the certain concentration levels are not allowed. This study estimated the flows of plastics originated from WEEE in their recycling process in Japan and the contained BFRs.⁴

First, the plastics generated from WEEE were estimated from the data of the end-of-product generation and the proportion of plastics in the WEEE. Next, the generated WEEE plastics were assigned to each recycling and disposal destination. The flows of plastics in each stage of the processes were then estimated by multiplying the amount of plastics processed with the distribution ratio for each recovered fraction. The flows of contained BFRs were estimated by converting the estimated flows of WEEE plastics by using the BFR concentration and the distribution ratios at each stage of processes.

The results showed that the mainstreams of WEEE plastics in the domestic WEEE recycling and treatment in Japan were the recovered mixed plastics or shredder residues. A large proportion of the recovered mixed plastics were exported from Japan in FY2017. Estimated flows of WEEE plastics and BFRs in Japan in FY2017 are shown in Fig. 4. It is possible that the amount of exported mixed plastics has significantly decreased after FY2018 due to China's waste plastic import ban, but interviews with plastic recyclers revealed that recycled pellets from WEEE plastics were still exported to China and other Asian countries. The results also showed that during the recycling and disposal process before incineration, a large proportion of the BFR-containing plastics in the bulk mixed plastics were removed by wet specific-gravity separation and X-ray sorting, indicating that a large proportion of the BFRs contained in the original mixed WEEE plastics were removed from the recycling chain.

POINT: A nation-wide municipal waste management model was developed for evidence-based policy making, especially for national target setting. The current recycling rate target of 28% in 2025 was proven to be unachivable. In the era of population decrease, policy mix of the promotion of recycling of food and plastic wastes and the reduction of incineration capacity is necessary, and ambitious policy implementation enables 23% of recycling rate in 2030.

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Population decrease occurs unevenly geographically. In the recent years, it is becoming more important to link the target setting of 3R (Reduce, Reuse, Recycle) policies at national level with policy implementation at municipal level. We therefore developed a municipal waste management model - referred to as the MINOWA (Municipality-Input Nation-Output WAste management) model (Tasaki et al., 2020) to estimate waste flows in Japan on the basis of a bottom-up approach, in which municipal solid waste (MSW) management data for each municipality are used and aggregated to the national level. As shown in Fig. 1, the MINOWA model consists of three sub-models: household waste generation and collection, business waste generation and collection (excluding industrial waste), and waste treatment and disposal (including recycling). Using the current (2015) and projected (up to 2030) populations, the MINOWA model simulates how different policies of 1,741 municipalities affect national-level policy outcomes, such as the amounts of recycling, final disposal, and greenhouse gas (GHG) emissions, in an integrated manner by taking into account regional characteristics. On top of business-as-usual scenario, the outcomes of waste prevention, food waste recycling, plastics waste recycling scenarios as well as all combined policy scenario were calculated for the entire country with consolidating measures of waste incinerators. Since extensive data is required for the model calculation at present and future projection of input parameters of the future, we created a database named "Japan Municipal Waste Database (J-Waste DB)" consisting of long-term data from 1971 to 2016 in collaboration with Ministry of the Environment, Japan (MoEJ) and Japan Waste Management Association and publicized it on our research center's web site.

In the era of population decrease, the operation rate of waste treatment facilities will decrease, and financial situation of municipal waste management will worsen. We estimated the decline in operating rates of incinerators in Japan for the last two decades (Tasaki et al., 2019), and proposed consolidation of waste incinerators as an option to retain efficiency of municipal waste treatment. Figure 2 shows areas where incinerators can be consolidated by 2030.

POINT: Support needs for the elderly in waste disposal were clarified through field surveys, and a guidebook was published to support local governments and community-based organizations (CBOs) in designing and operating effective programs on this issue.

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There are at least two age-related challenges observed in waste management of Japan. The first issue is that elderly have difficulties in taking out the trash. The core of this issue is that an increasing number of elderly people find it difficult to take out the trash, but they are unable to receive the support they need (Kojima and Tajima, 2019). The inability to take out the trash by elderly people can lead to three different consequences: a) storing the trash in the house, b) taking out the trash improperly, and c) continuing to take out the trash even though it is too difficult. Based on the research outputs from the previous NIES five-year plan term and consultation with waste management experts, we published a guideline available both in Japanese and English online for municipalities to cope with issues related to waste disposal by the elderly. Our guideline explains the issue in detail, and gives principles, procedures, and practical advice on introducing ways to support elderly resident by means of public and community support. We also published a report (in Japanese) that introduces 12 good practices for supporting waste disposal by the elderly. The guidebook has been referred to in national and municipal policy making, as well as in news reports and activities of local communities.

The second issue is maintenance of waste collection points. In Japan, municipal waste is collected by municipalities typically from waste collection points that are installed and operated by neighborhood associations. Aging is considered to have negative impact on these activities since neighborhood associations are commonly steered by elderly people. In order to propose an ideal way to manage waste collection points in aging society, we interviewed officials from local municipalities and conducted a questionnaire survey and interviews with community leaders in Tsukuba city.

The results revealed that neighborhood associations are playing a key role in the management of waste collection points, such as raising awareness of waste disposal rules, assigning waste collection point cleaning duties, and collecting and separating inappropriately disposed waste. In addition, more inappropriate disposal was reported in areas where waste collection points are not managed by neighborhood associations. The results also showed that in areas with a higher percentage of elderly residents, more elderly people are unable to participate in their assigned waste collection point cleaning duties, experience difficulties in sorting and taking out their waste, and chose to withdraw from neighborhood associations. As for regional differences, elderly people tend to be more isolated in large-scale residential areas than in rural areas. These results suggest the need to introduce alternative methods to maintain waste collection services in aging society, taking local situations into account.

POINT: There were six patterns of quality improvement of resource circulation, and our attempt to quantify social values of a pattern confirmed its importance as well as methodological issues. Consumers' expected lifetime of electrical and electronic equipment was different from the actual lifetime by 50%, and effectiveness of the improvement of product durability was limited to 30-60% of cases examined.

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To improve the quality of resource circulation and reduce the natural resource consumption by extending product lifetime, we reviewed advanced cases that enhance the value creation and quality resource use. Approximately 50 cases were categorized into six types (upcycling products, material recovery, natural decomposition, social value creation, community revitalization, and online market). These included cases of the utilization of previously unused and discarded resources and the creation of social value (e.g. creating jobs for disabled people). We also developed a product lifetime model that can quantitatively analyze the impacts of the promotion of longer-use of products (Oguchi et al., 2019). The results showed that if the number of consumers who used their durable products for 1.4 times longer than normal consumers were to increase to 20% of all the consumers, product demand and end-of-life product generation would decrease by 5% to 10%.

POINT: Guidelines on composting and mechanical-biological treatment (MBT) were developed to assist decision-makers, policy-makers and other stakeholders in Asia in evaluating feasibility of these methods as strategic options for improving local waste management systems.

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Many developing countries fully rely on open dumping or uncontrolled landfilling in their municipal solid waste (MSW) management practices because it is less expensive to construct and operate these sites. However, the direct disposal of untreated organic waste in open dumping or landfill sites has indisputable environmental impacts at both local and global levels.

Composting is one of the best options to reduce the environmental impacts at dumping sites as landfilling of organic matter can be avoided. PJ4 developed a guideline on composting (Kawai K. et al., 2020) (Fig. 1) focusing on the introduction of composting projects based on source separation of organic waste and aerobic fermentation at plants for MSW management in the cities of developing Asian countries. PJ4 also developed a guideline on the introduction and implementation of MBT technology (Ishigaki T. and Liu C., 2020) (Fig. 1) targeting its application in Asian cities as MBT also has advantages in terms of resource circulation, less environmental impact, and cost efficiency. These guidelines are expected to assist decision-makers and policy-makers in Asia in evaluating feasibility of introducing these methods and sustainably implementing them for improving local waste management systems.

POINT: Energy-saving and decentralized waste and wastewater treatment technologies were developed and adapted for their wider application in Asian countries. Performance-testing, evaluation and certification systems for the treatment facilities were also proposed to specific countries in order to highlight technical and financial efficiencies of these technologies and promote their dissemination.

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As part of PJ4's research into the establishment of a watershed management system that uses energy-saving and decentralized waste and water treatment technology, characteristics of a decentralized waste and wastewater treatment system in a rural area of China were investigated and analyzed. More specifically, anaerobic digestion of livestock waste in the rural areas was studied with the focus on evaluating the effects of temperature on the dynamics of antibiotic resistance genes (ARGs) and microbial communities. The results of our analysis clarified the cooperativity of gene transfer-related items on ARG variation, and proved that higher temperature will not always achieve better ARG removal in anaerobic digestion unless pathogens and gene transfer elements are more efficiently inhibited. The findings are expected to contribute to improving efficiency of the livestock waste treatment system. We proposed introducing the technology and equipment to rural areas according to their respective regional and drainage characteristics. In addition, we proposed necessary regulations for the rural areas regarding the standard establishment, maintenance and management, and performance evaluation systems.

Progress in our research on the performance-testing, evaluation and certification systems for the domestic wastewater treatment facilities was made mainly for Indonesia. With input from stakeholder meetings in Indonesia, we drafted a performance-testing method. A trial of the testing method was conducted to confirm the feasibility of the testing procedure (Fig. 2). Japanese wastewater treatment technologies were also tested under high temperature and with a typical Indonesian inflow pattern. This pilot test revealed greater treatment efficiencies and lower sludge generation under these typical Indonesian conditions; this should reduce both the initial capital outlay and the operating costs.

POINT: PJ4's study on the establishment and commercialization of a waste management system in harmony with urban planning proposed a business model for the phased introduction of resource recovery and sanitation facilities during the development of luxury residential districts or large commercial facilities in emerging Asian countries.

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The proposed business model sets up the following three phases for the phased introduction of resource recovery and sanitation facilities: (1) a phase of management at the time of discharge, such as source separation; (2) a phase in which relatively simple facilities such as resource recovery facilities are introduced; and (3) a phase in which the incineration plant, sewage treatment plant and piping system are installed to integrate waste treatment, wastewater treatment and hot water supply (Fig. 3). For the last phase, a model was developed to estimate the balance of these materials, energy and cost-benefit. The amount of willingness to pay was assessed through a questionnaire survey in the suburbs of Hanoi, Vietnam. We acquired a registered trademark (Fig. 3) and discussed with the relevant entities to show the various factors involved in the implementation of the project.

POINT: Development and adaptation of various MSW management and treatment technologies were examined, and the ones that suit Asia-specific situations (including Japan) and contribute to establishing a robust, sustainable and integrated waste management system in the region were identified.

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To develop landfill leachate treatment suitable for Asia, PJ4 evaluated the feasibility of constructed wetlands (CWs) by the field experiment at a landfill site in Thailand (Ogata Y. et al., 2018). The evaluation results revealed that CWs can effectively remove recalcitrant organic substance and nitrogen from landfill leachate for long-term. The removal mechanism was mainly microbial reaction with combination of accumulation in media and promotion by plant. Our results indicate that the use of CWs is a promising sustainable leachate treatment method.

Moisture retention capacity and adhesiveness derived from organic waste, one of the major components of Asian MSW, have lowered efficiencies of intermediate treatment and resource recovery. The adaptation of the operation of treatment technology to the regional characteristics as well as stable organic waste recycling scheme by implementing the segregation will be essential to resolve this problem. Quality of the solid recovered fuel (SRF) produced by MBT in Asia is often lower than that of the internationally distributed one, and the consumers often need to refine the product further due to the fluctuations in its quality. This situation has become a barrier to enhancing the use of SRF and appropriate regional waste management. Our analysis of heat and carbon balances in the MBT process exhibited the possibility of effective drying by maximizing the evaporation, and it contributes to improving the SRF quality (Sutthasil N et al., 2020).

Production of biochar from MBT residues was considered to be an effective way to reduce its landfilling amount. Biochar made from MBT residues had high specific surface area and high ratio of micropores (<2mm) and it showed higher adsorption capacity of heavy metals in wastewater. Comprehensive evaluation on environmental impact of the whole waste management system revealed that the implementation of MBT and semi-aerobic management of the landfill site could lead to the highest reduction of greenhouse gas emissions. It ascribed to the reduction of direct emission of methane from disposal site and substitutional reduction of carbon dioxide by SRF use.

As mentioned earlier, we developed a guideline on the implementation of MBT (Ishigaki T. and Liu C., 2020) in the cities of developing Asia to assist decision-makers, policymakers and other stakeholders in evaluating the feasibility of MBT as an appropriate strategic option for improving the local waste management system (Fig.1).

POINT: Long-term environmental safety of the waste containing hazardous materials was investigated by evaluating effectiveness of various disposal and shielding methods used in landfills. Based on our findings, structural and waste disposal requirements were presented for landfills to improve long-term environmental safety.

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PJ4 studied the environmental safety of the waste shielded by various barriers, and presented that the disposal method with geological barriers set the allowable amount of transfer in the environment. For mercury, dissolved mercury that can be emitted from the sulfide and solidified form of mercury-consisting waste can also be transformed and behaved as gaseous mercury by volatilization at the gas-liquid interface under unsaturated conditions of the isolated monofill with limited water penetration. We found that the maximum flux of dissolved mercury and gaseous mercury can be reduced, and the time of emergence will be managed for a long term (thousands of years level) by isolated monofill with control of internal infiltration and the adsorption layer (Ishimori H. et al., 2020).

Our study focused on other heavy metals as well as mercury. We developed a numerical landfill model taking the phenomena mentioned above into account. The results were coupled with the crack propagation analysis, which represented the deterioration of concrete due to neutralization and saline damage and the physical damage caused by a large-scale earthquake, to quantify the environmental safety of landfilling on a 100-year scale. We presented structural and waste disposal requirements to improve the long-term safety of the landfills for hazardous waste as an outcome of our examinations.

POINT: We developed a small-scale biogas production system that can significantly improve energy recovery efficiency using anaerobic co-digestion of food waste with fat, oil and grease.

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Anaerobic co-digestion with oily waste is a promising way for enhancing the energy efficiency of biogas plants, since fat, oil and grease (FOG) give high methane yields during anaerobic digestion (Kobayashi et al., 2017; Wu et al., 2018). We selected one high-productivity technology from the developed co-digestion methods, and then applied it to a bench-scale apparatus of a small-scale on-site system installed in a high-rise building in the center of a Japanese city. The system was designed to generate biogas from food waste and wastewater that include a high concentration of locally produced FOG.

To enhance the energy recovery efficiency of the installed biogas system, we investigated anaerobic co-digestion of FOG in semi-continuous experiments. Despite the increased production of methane, a high mixture-ratio of grease trap waste to food waste inhibited microbial activity. The key substances in this inhibition were long-chain fatty acids (LCFAs); the accumulation of LCFAs eventually led to process failure (Wu et al., 2017; Kobayashi et al., 2020). The results of a comparative study using two laboratory-scale anaerobic reactors called mesophilic and thermophilic continuously stirred tank reactors (CSTRs) at different temperatures (35℃ and 55℃) suggested that mesophilic microbial consortia had greater tolerance to high lipid loading than did thermophilic consortia.

Further, we conducted a semi-continuous experiment on anaerobic co-digestion using a continuously stirred fluidized bed reactor (CSFBR) in an effort to achieve both high process stability and high volumetric organic loading rate (OLR) under thermophilic conditions. Methane production using the CSFBR was almost the same as that using the thermophilic CSTR. However, the CSFBR maintained much lower concentrations of volatile fatty acids and LCFAs than did our previous mesophilic and thermophilic CSTRs. These results demonstrated that the CSFBR simultaneously provided high process stability and capacity for high OLR in the co-digestion of food waste and oily waste. This CSFBR will help substantially to enhance the energy recovery efficiency of small-scale on-site biogas production systems for urban uses.

In addition, we developed a fugacity model to represent the behavior of organic pollutants such as polybrominated flame retardants (e.g. polybrominated diphenyl ethers, or PBDEs) in actual biogas plants. We measured the partition coefficient between water and dissolved organic carbon (KDOC) of PBDEs (Shi et al., 2019a), and also analyzed degradation behavior of PBDEs in anaerobic digestions of food waste (Shi et al., 2019b). Furthermore, we modified the model by using the KDOC values, and showed that the modified model successfully represented the actual fate of PBDEs in the biogas plant. This modelling will be useful for taking countermeasures when the pollutants are transported to biogas plants.

POINT: Elemental composition of various incineration residues was analyzed to clarify behavior of useful and harmful metals during incineration of MSW and woody biomass. A method combining air-table sorting with particle size and density separations was found to be effective for recovering precious metals from bottom ash.

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Regarding WtM technologies, we analyzed the elemental composition of each type of MSW to be incinerated, including wood, paper, and plastics. Contribution of each waste category to the useful and harmful metals in incineration residues was estimated. Following this, we investigated the behavior of useful and harmful metals in several MSW thermal treatment facilities and a woody biomass power generation facility. For example, at a fluidized-bed-type incineration facility, fluid sand, boiler ash, gas cooling-tower ash, and air-pollution control residue were sampled, and an elemental composition analysis of the samples was then performed. The major components of fluid sand and other types of ash proved not to differ largely, except in the case of volatile elements. Meanwhile, we investigated the elemental balance during incineration of woody biomass in the biomass power generation facility, the number of which has significantly increased recently resulting in generating a large volume of the incineration ash. The behavior of various elements from fuel wood tips to grate ash, bottom ash, and fly ash was clarified. Furthermore, X-ray diffraction measurement and elemental composition analysis were performed on bottom ash, fly ash, fuel chips, and other materials collected at the woody biomass power-generation facility to clarify their mineral composition and better understand elemental behavior in the facility. These data are useful for developing recycling methods of the incineration residues from biomass power generation facilities.

In addition, as a resource recycling method for MSW incineration ash, we proposed a draft method in which metallic particles are separated by using an air-table sorting apparatus and aging of the separated ash residue is accelerated by ventilation with a gas enriched with carbon dioxide (CO₂). An air-table sorting device was introduced to sort MSW bottom-ash particles according to their size and density (Back et al., 2020), and dependence of the elemental composition of the ash particles on the particle size and density was clarified (Fig. 2). Since the metal particles are not crushed during the ash crushing process, this new method is effective in terms of recovering the metal particles with enrichment of precious metals such as gold and silver.